Demand Media, the online media firm headed by former MySpace chairman Richard Rosenblatt, said today that it has acquired Pluck, a provider of social media software for publishing firms. Austin, Texas-based Pluck's software is used by Reuters, Hearst, Gannett/USA TODAY and other publishers to find and feature blog posts. Financial terms of the acquisition were not disclosed. Pluck was founded in 2003. Demand Media has raised over $350 million in venture funding for its social media efforts.